The subject invention relates generally to combustors. More particularly, the subject invention relates to the introduction of diluent flow into a combustor via a fuel nozzle.
Combustors typically include one or more fuel nozzles that introduce a fuel or a mixture of fuel and air to a combustion chamber where it is ignited. In some combustors, the fuel nozzles extend through holes disposed in a baffle plate of the combustor. In these combustors, it is often advantageous to introduce a volume of diluent, often nitrogen or steam, to the combustor to reduce NOx emissions and/or augment output of the combustor. The diluent is urged from a chamber through a gap between the baffle plate and each fuel nozzle, and then flows along a periphery of the fuel nozzle where a portion of the diluent enters the fuel nozzle via holes in the air collar of the fuel nozzle. The gaps between the baffle plate and the fuel nozzles, however, vary due to assembly tolerance stack-ups between the baffle plate and the fuel nozzles. The gap variation results in variation in diluent flow around each nozzle and throughout the combustor assembly. Further, an axial distance between the gap and the air collar holes in the fuel nozzle allow diluent to reach the combustion reaction zone without passing through the fuel nozzle and mixing directly with the fuel and air. Both of these effects reduce diluent efficiency and therefore a greater volume of diluent is required to achieve an equivalent amount of diluent flow into the fuel nozzle. The excess diluent that flows toward the combustion reaction zone without passing through the fuel nozzle leads to operability problems in the combustor such as dynamics and blow out.